Natural
HistoryDrosophila
melanogaster, or the red-eyed pomace
fly, is classified in the family Drosophilidae, and order Diptera (which
also includes flies, mosquitoes and midges.)

In the wild, they are found near ripe fruit where the adults and larvae
feed on yeast and bacteria growing on rotting fruit. In the lab, they
can be fed on yeast cells growing on a high carbohydrate prepared diet.

The average life span of Drosophiladepends
on the environmental conditions. There are records of 80-153 days, but
the average life span of a Lab fly is 26 days for a female, and 33 days
for a male. (Under crowded conditions this may be reduced to 12 days.
Also mutant flies generally have a shorter life span). Temperature
greatly effects the rate of development. At room temperature (25˚C):
10 days from egg to adult; at 20 ˚C: 13 days; at 15˚C: 90 days.
There are four phases to the life cycle: egg - 3 larval (instar)stages
- pupa - adult.

Courtship begins by the male tapping the abdomen of the female with his
foreleg. This is his means of identifying his own species. He approaches
the female fly from the front, and circles around her making half turns.
He sticks a wing out, vibrating it for several seconds. If the female
is receptive, copulation results. Sperm from the male are held in the
seminal receptacle or spermatheca. There may be more than one mating.
Eggs are .5 mm long, and are laid generally after the third day of the
female’s adult life.

Larvae hatch in 22 hours, and grow and feed for four days, (longer at
lower temperatures). The larvae are transparent, and one can see the inside
organs such as the coiled intestines, whitish fat bodies, and gonads (visible
in the male but very small in the female). During the third instar stage
of larval development, observers of Drosophila will notice the larvae crawling up the sides of the
culture container in preparation for pupation. At this time one can see
dark projections called pupal horns, off the anterior end. These are the
spiracles (outside opening of the respiratory tubes) turned inside out.

The pupal case forms, darkens and hardens. Sexing of the pupae can be
done by looking for tarsal sex combs of the male, visible from the ventral
side. The sex combs in the adult males, are tufts of dark hair found on
the most proximal tarsal joint of the foreleg, used for holding the female
during mating. Even in the pupal phase, these dark patches are visible
in males.

The pupal stage lasts for 4 - 6 days, during which time metamorphosis
occurs. Larval tissues are broken down (except for the brain and a few
other tissues), and imaginal discs (pockets of cells stored in the larvae)
develop into adult organs. There is a disc for each leg, wing, eye, antennae
etc. Finally the pupa is ready to eclose (emerge) into the adult
stage. Adult Drosophila males
and females can be easily distinguished. Males are smaller, with a rounded,
blackened tip to their abdomen (posterior segment). Females have a pointed
abdomen, with a pattern of even dark bands.

RearingRaising Drosophila
in the classroom is easy and inexpensive. It is wise to keep the
cultures at room temperature, and to keep the culture vials or tubes humidified.
(A small, moistened piece of filter paper, or water at the bottom of the
rack in which the culture tubes rest will do this job.) Subcultures
can be made at any time, but adults should at least be transferred to
fresh medium every 20-30 days to avoid problems with mites and mold. Overcrowding
slows developmental time because of competition for food and a place along
the side of the tube to pupate.

When raising mantids, a large and continual supply of fruit flies is
needed. To do this set up several culture vials (subcultures) every
two weeks. Getting your culture started is the hardest part. Preferably
before your mantids start to hatch, order or obtain 2-3 vials of feeder
Drosophilafrom one of the biological supply
houses. (Note that the mantids can go for a couple of days without
food as long as you keep their cage humid). Once the flies arrive,
set up about 4 fresh vials placing approximately 10 flies in each, and
set them aside. Keep the remaining flies in the vials they were
shipped in and use them for mantid food. You may want to set up
4 additional vials the following week to jump-start your colony, but after
that you need only set up 4 vials every 2 weeks. This should give
you plenty of flies for each egg case hatched. Keep all your vials (labeled
with the date they were set up) in a plastic shoe box in rows with new
vials at one end and older vials at the opposite end. Freeze vials and
any remaining flies when the media gets dark, moldy and/or dries out.
You can cut this whole operation back to 1 or 2 vials once your mantid
nymphs are ready to take on larger prey. You may want to keep 1
or 2 vials going the rest of the year so that you have a starter culture
the next spring. If you take care of them well, you may not need
to purchase any new flies the following year. Just plan to step
up your fly culturing operation in the early spring before you purchase
your mantid egg case.

Note: the biological supply houses all carry flightless Drosophilamelanogasterfor feeding
small animals. Some suppliers also carry a larger species such as
D. hydei (flightless) and D.
virilis(a hardy species, but they do fly).
These are usually too big for some mantid species when they first hatch,
but work great when the nymphs get a little larger. You might want
to keep a culture of both D. melanogaster and D. hydei.

Since fruit flies are so small, it’s best to handle them with a
small paint brush or not at all. When feeding mantids, you can just
gently pour and tap flies into the mantid cage. This works well
with flightless fruit flies. If you capture your own wild flies
(which can easily fly out of your rearing vials) you may need to chill
them in the refrigerator for a few minutes before tapping them into the
mantid cage.